Wireless expansion scheme of WCDMA network

In the initial stage of 3G construction, the operators mainly focus on solving the problem of network coverage, but it is necessary to consider the future Evolution mode of network capacity from the angle of network planning and equipment selection, because only when the technical characteristics of WCDMA are fully considered in the initial phase, the reasonable network structure and construction direction are determined. In order to ensure network performance and reduce construction costs of long-term goals, avoid detours.

The following is a brief analysis of several alternatives for WCDMA wireless network expansion process.

Plan one: Large-scale division of the community, that is, the initial focus of the construction of the network is to solve the cover and reduce the initial investment, so the site spacing is large, later with the increase in user density, must be implemented in a certain way to achieve site encryption, the original cell division into more coverage of smaller areas The limitation of this scheme is that the base station cover should be adjusted in a large scale, and the station site should be determined for a lot of new stations; compared with GSM, WCDMA network capacity is more sensitive to the regularity of honeycomb structure, more stringent to station site and antenna height, and requires large-scale redesign of network.

Scheme two: A large number of micro-cellular, deployment of layered Network (HCS), the macro-honeycomb and micro-cellular settings to different levels, the use of specific cell re-election or switching algorithms, will be in the idle or connected mode of users to the macro honeycomb or micro-honeycomb layer, the two layers using different carrier. The limitation of this approach is: when the operator has only two or 3 carriers (that is, 10 or 15MHz), in the premise of not fully play the capacity of the macro-cellular base station, the use of specialized carrier deployment micro-honeycomb layer, from the perspective of investment analysis, and because in the absence of adequate isolation, The micro honeycomb layer and the macro honeycomb layer cannot share the same carrier; if the continuous coverage of the micro-honeycomb layer can not be achieved, the frequent operation of compression mode will cause the waste of system capacity and reduce the uplink coverage, if the frequency measurement is not enough timely and sufficient, it may also increase the probability of losing the speech due to the hard switching failure.

Scheme III: The original base station to expand to Multicarrier, the premise is that operators have multiple carriers, the solution advantage is: The lowest cost of expansion, compared to the first two ways, do not need to create a new base station, do not have to add expensive power amplifier (PA). From the first day of network deployment, many manufacturers NodeB PA has been able to support Multicarrier, as long as the original NodeB in accordance with capacity required to increase the baseband channel unit module and transceiver module, and baseband channel module can be shared between multiple carriers, improve the efficiency of the use, The number of channel units required for each carrier is reduced in disguise; the expansion effect is obvious, in the case that the base station power reserve is big enough, the wireless capacity increases exponentially with the increase of the carrier number of the base station, and when the Multicarrier Service allocation (MCTA) function is introduced, the wireless capacity of the whole system can obtain the additional reuse gain, the minimum capacity of the project The original base station layout and day feeder system (including antenna angle, height, etc.) do not need to make a big adjustment, maintain the original network structure also helps to ensure that the network performance is running stable, greatly reduce the workload of optimization; The switching between carriers is easier to solve, and Multicarrier still uses the original antenna system configuration, If PA power is evenly distributed among multiple carriers, then the coverage of each carrier has a strong correlation between the carrier, when the hard switch between carriers, because the target cell is relatively clear, almost without the different frequency measurement can be successfully implemented hard switching, so as to avoid the negative impact of the startup compression mode, At the same time, it has a high success rate of hard switching, which has been fully validated in the long term CDMA network business practice. (Computer science)

This shows that the mode of Multicarrier expansion should be the first choice for WCDMA network expansion, which is consistent with the experience of the second generation of CDMA network, and the deployment experience of GSM network is different.

Although the capacity of GSM network based on TDMA is lower than that of CDMA network, but it is relatively fixed, frequency is more frequent, there is frequency multiplexing distance, it is easy to use reserved frequency point to increase base station, and the working characteristic of terminal non continuous transceiver makes the hard switch based on the different frequency measurement very simple, This is also the basic operation that must be done in the trans-cell movement process.

WCDMA belongs to Wideband spread spectrum technology, frequency (5MHz) multiplexing coefficient is almost 1, the network performance and capacity are greatly influenced by the interference control, so the base station layout, antenna height and so on are more stringent. Mobility is mainly through soft switching, and the influence of different frequency measurement on network performance and communication quality is relatively large and should be controlled.

The preferred Multicarrier expansion scheme is recommended, and does not imply an absolute rejection of other modes of expansion.

Nortel Network typical Acer cellular base station BTS12000 in a base cabinet can support 1 to 6 45W of ultra linear Multicarrier power amplifier (MCPA), each MCPA can support 4 carrier, namely 20MHz bandwidth. That is, the power reserve from 45W to 270W is provided in the single cabinet, which realizes the smooth evolution of the maximum capacity of three carrier three sectors, and satisfies the long term traffic growth demand from the Omni-Station or OTSR configuration mode of single carrier single sector area.

Perhaps some people think that the use of high-power PA will increase the interference between the base station, to increase the capacity does not help, this is actually a misunderstanding. Since WCDMA base stations are not always fired at the maximum power, in addition to overhead channels such as the common pilot channel, the actual output power of the business channel part is based on the number of users being talked, the wireless bearer type, the user location and the traffic environment. In fact, the higher the power reserves of the business channel, the lower the loss caused by power shortage, the greater the wireless capacity.

According to the relevant simulation research, compared with S111 (45W per load fan) wireless capacity, S222 (22W per load fan) is 1.8 times times, S333 (each fan 15W) is 2.4 times times, S333 with emission diversity (per load fan 90W) can reach 3.5 times times. The carrier capacity is mainly limited by the available power of each load fan, while the capacity loss caused by adjacent channel interference can be neglected (less than 1%). In the first three phases, only 3 PA per base station was introduced and the launch diversity was added to 6 Pa. However, low power PA can not achieve satisfactory capacity effect.

At the same time, if the use of Low-power or single carrier PA configuration base station products, there are several shortcomings, including: In the future expansion process with

The increase in the number of carriers, the cost of power amplifier is linearly increasing; with the increase of PA and the number of road-hop, the slot of single cabinet is often unable to meet the need, to increase the expansion cabinet; merging the amplified signals will result in additional joint insertion loss, resulting in waste of energy and reducing the effective output power.

In CDMA commercial networks, the 54W Multicarrier RF module (MFRM) of Nortel Networks has been widely deployed in tens of thousands of cdma/cdma2000 base stations. Since the 2000 Nortel Network in Wcdmanodeb to take the lead in the use of high-power MCPA, the industry's other manufacturers have also planned to introduce similar products to meet market demand.

Due to the use of special patented algorithm in RF module, Nortel Network MCPA Power amplifier efficiency of more than 12%, thereby significantly reducing the power consumption of the base station, currently in the industry the lowest power consumption, reducing the requirements of the refrigeration system and the operating process of electricity expenditure.

Whether it's a new wireless carrier or an existing 2G operator, in the upcoming 3G network construction process, faced with wide coverage, large capacity, high data rate, low-cost scalability, such as some of the objectives, we must reasonably choose product solutions and networking strategies to keep competitive advantage.